The present invention relates to a curable silicone composition. More particularly, the present invention relates to an organopolysiloxane composition capable of undergoing both addition and condensation reactions.
As conventional curable silicone compositions there are known organopolysiloxane compositions of the addition reaction type and the condensation reaction type.
The organopolysiloxane composition of the addition reaction type is characterized in that an organopolysiloxane having an alkenyl group and an organopolysiloxane having a hydrogen atom bonded directly to the silicon atom are cured by a catalyst for the addition reaction such as a platinum compound (see, for example, Japanese Patent Publication No. 27853/1968). This composition is advantageous in that since no by-product is formed in the curing step, the composition is uniformly cured even to the interior and since the curing degree is controlled by heating, the curing time or serviceable life can be adjusted. Accordingly, this composition has been broadly used, mainly as a potting or coating material for electric and electronic parts.
The organopolysiloxane composition of the condensation reaction type is characterized in that a hydroxyl group-containing organopolysiloxane and a hydrolyzable crosslinking agent are cured by a tin compound or the like (see, for example, Japanese Patent Publications No. 16798/1963 and No. 21631/1965). This composition is advantageous in that since the composition is cured at room temperature by the moisture contained in air, the processability is good, insufficient coating is hardly caused and if absorption of the moisture is prevented, the composition can be stably stored in one package. Accordingly, the composition is used as a sealant for construction, an industrial adhesive, a potting material, a coating material, a mold-making material and as a roller of a copying machine.
However, the known organopolysiloxane compositions of the addition reaction type are defective in that insufficient curing is caused on a surface containing a catalyst poison such as a compound of nitrogen, phosphorus, tin or sulfur. Thus the composition cannot be used on such a surface. The composition is ordinarily of the two-package type, but if a reaction regulator or the like is used to change the composition to a one-package type, heating at a relatively high temperature is necessary for curing. Moreover, since the amount of the catalyst is reduced so as to maintain good stability at room temperature, insufficient curing often results.
The known organopolysiloxane compositions of the condensation reaction type are defective in that since the composition is cured by moisture, the interior is not promptly cured even after the surface has been cured. Even if heating is performed so as to promote curing, no substantial promoting effect can be attained. Therefore, although the compositions of this type are excellent in processability, the composition is disadvantageous in that the composition can be used only for situations requiring relatively small thickness.
The object of the present invention is to overcome the defects of the above-mentioned organopolysiloxane compositions of the addition reaction and condensation reaction types. More specifically, it is a primary object of the present invention to provide a curable silicone composition in which the defects of organopolysiloxanes of the addition reaction type, that is, insufficient curing and the necessity of heating for curing in the case of one-package type compositions, and the defects of organopolysiloxane of the condensation type, that is, delayed curing of the interior and no substantial promotion of curing by heating are eliminated, while only the merits of the organopolysiloxanes of the addition reaction and condensation reaction types are retained. In other words, the present invention provides a curable silicone composition in which insufficient curing does not result, curing is advanced at room temperature even in the case of a one-package type composition and curing is promoted by heating.